We investigated the interactions of platinum metal clusters on the gamma-alumina using a periodic density functional theory method. Results showed that electron transfer occurs between platinum metal clusters and gamma-Al2O3. We also investigated NO adsorption properties (NO-Pt-4/gamma-Al2O3) in order to clarify the support effect on NO activation in terms of the elongation of N-O bond length and NO molecular charge. In our results, the support increases NO activation for three-fold sites but decreases it for on-top and bridge sites. Moreover, the support changes the site preference of NO adsorption. In addition, in order to clarify the support effect at finite temperature, we studied the dynamic behaviors of supported precious metal catalysts by using a tight-binding quantum chemical molecular dynamics program named 'Colors'. (c) 2006 Elsevier B.V. All rights reserved.